The present invention relates to a ballast circuit for gas discharge lamps. More particularly, the present invention relates to a ballast circuit having means for reducing electromagnetic interference (E.M.I.).
Recent improvements to the incandescent lamp art have provided an improved lighting unit having a highly efficient gas discharge tube as a main light source and an incandescent filament as a supplementary light source. Such an improved lighting unit is generally described in U.S. Pat. No. 4,350,930 of Piel et al, issued Sept. 21, 1982.
The gas discharge tube may be successfully operated by a ballast circuit developing a D.C. operating voltage for the gas discharge tube. Such ballast circuits are described in the previously mentioned U.S. Pat. No. 4,350,930 and also U.S. Pat. No. 4,320,325 of T. E. Anderson, issued Mar. 16, 1982.
The gas discharge tube has various modes of operation such as, (1) an initial high voltage breakdown mode, (2) a glow-to-arc transition mode, and (3) a steady state run mode. A ballast circuit, such as described in U.S. Pat. No. 4,350,930 for operating the gas discharge tube has an operating circuit having a starting circuit which employs a triggering oscillator that provides the necessary voltages so as to transition the gas discharge tube from its (1) initial high voltage breakdown mode, (2) to its glow-to-arc mode, and then (3) its steady state run mode.
The starting circuit due to its triggering oscillator typically generates a relatively high spiked pulse signal, which, in turn, typically generates a commonly known electromagnetic interference (E.M.I.) signal that is coupled onto the A.C. line supplying the incandescent unit and is manifested, for example, as a distracting signal which affects television viewing.
Filtering circuits that reduce or even substantially eliminate the electromagnetic interference type signals are well known. E.M.I. filters typically comprise an inductor-capacitor parallel arrangement. EMI filters employed for relatively low frequency applications, such as 50 to 60 Hz, require relatively large values for the inductor and capacitor circuit elements. The relatively large values of capacitors and inductors, in particular the large inductors, are disadvantageous with regard to the placement of these inductors within the housing of a relatively small device such as an improved lighting unit. It is desired that means be provided for an improved lighting unit that reduces the electromagnetic interference without the need of employing relatively large values of inductive and capacitive circuit elements.
Accordingly it is an object of the present invention to provide means for reducing electromagnetic interference without the use of inductors and enabling use of relatively small capacitors.
These and other objects of the present invention will become more apparent upon consideration of the following description of the invention.